Connection error

An unexpected error occurred.

UNKNOWN_CONNECTION_ERROR

Symptoms

  • The error banner shows a generic "Connection error" without a specific cause.
  • The technical details show a message that carried no error type or status we recognise.

Likely causes

  • The failure arrived with nothing to identify it by. MCUHex reads the exception type, the probe’s own numbered status and the chip’s reported state — this page means none of the three said anything definite.
  • A probe or an OS-level USB quirk we have not seen. Sending you after the wrong fix costs more than admitting the failure was not understood, so nothing is guessed here.
  • An older MCUHex tray app. Versions before the error classifier reported most connection failures this way; updating the tray app alone resolves many of these.

How to fix it

  1. Update the tray app

    If the tray app is older than the current release, most failures that land here already have a named guide in the current version.

  2. Read the technical detail

    Expand the error’s technical message. It is passed through from the debug layer unchanged, so it often names the real cause even when we would not commit to a code.

  3. Run the standard triage

    Replug the probe, restart the tray app, refresh the page, retry. This clears one-off USB failures.

  4. Report it

    If it reproduces, send us the technical message via the feedback form. Every failure we can name gets a guide of its own here; this page exists for the ones we cannot yet.

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